In female rats, vaginocervical stimulation (VCS) received during mating or parturition modifies sexual and maternal behavior and induces neuroendocrine changes which influence reproductive success. Mating is required to initiate the endocrine changes of early pregnancy, in particular, the twice-daily surges of pituitary prolactin (PRL) secretion which occur for the first 10-12 days of pregnancy or pseudopregnancy (PSP) and which maintain ovarian progesterone secretion. The particular characteristics of the VCS received by the female during a natural mating sequence determine whether PSP will occur, and both the number and the timing of intromissions received by the female have been shown to influence the initiation of the PRL surges. Data suggest that active patterning or pacing of VCS by the female during mating is critical for processing and storage of genitosensory inputs and that the intermittent and discontinuous stimuli resulting from paced mating maximize the likelihood that sufficient amounts of stimulation accumulate in brain for PSP. We have hypothesized that expression of these PRL surges is dependent both upon summation of individual stimuli throughout a single episode of mating and upon longer-term changes which perpetuate the expression of PRL surges over the subsequent 10-12 days. Previous work has characterized the natural mating stimuli which are optimal for induction of the PRL surges, determined which specific changes in PRL secretion are the direct consequence of such stimulation, established that the medial amygdala (MEApd) is an important integrative center for this response, and begun to examine whether and how glutamatergic and noradrenergic neurotransmission within the MEApd are involved in establishment of the neural mnemonic required for PSP. The experiments outlined in this application will use this model system to address the broader questions of how sensory stimulation is filtered to maximize retention of information and how sensory input induces neural plasticity which may alter brain function over the long term. This Independent Scientist Award renewal application proposes that the PI learn confocal microscopy with stereological precision and that she undertake a collaborative electrophysiological study examining responses of MEApd neurons to repetitive VCS. This plan will facilitate short-term goals (confocal work) and will explore avenues for addressing long-term research goals (electrophysiological project).